[lldb] Move clang-based files out of Symbol

Summary:
This change represents the move of ClangASTImporter, ClangASTMetadata,
ClangExternalASTSourceCallbacks, ClangUtil, CxxModuleHandler, and
TypeSystemClang from lldbSource to lldbPluginExpressionParserClang.h

This explicitly removes knowledge of clang internals from lldbSymbol,
moving towards a more generic core implementation of lldb.

Reviewers: JDevlieghere, davide, aprantl, teemperor, clayborg, labath, jingham, shafik

Subscribers: emaste, mgorny, arphaman, jfb, usaxena95, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D73661
diff --git a/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp b/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp
index f96a7dc..7264511 100644
--- a/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp
+++ b/lldb/source/Plugins/SystemRuntime/MacOSX/SystemRuntimeMacOSX.cpp
@@ -7,12 +7,12 @@
 //===----------------------------------------------------------------------===//
 
 #include "Plugins/Process/Utility/HistoryThread.h"
+#include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 #include "lldb/Breakpoint/StoppointCallbackContext.h"
 #include "lldb/Core/Module.h"
 #include "lldb/Core/ModuleSpec.h"
 #include "lldb/Core/PluginManager.h"
 #include "lldb/Core/Section.h"
-#include "lldb/Symbol/TypeSystemClang.h"
 #include "lldb/Symbol/ObjectFile.h"
 #include "lldb/Symbol/SymbolContext.h"
 #include "lldb/Target/Process.h"